A. Bernanose at the Nancy-Université in France published an article on electroluminescence in organic materials in 1953 for the first time in the world. Yet, the electroluminescent organic materials were not suitable for use as a display element as yet due to excessively high threshold voltage. In the meantime, Dr. C. W. Tang succeeded in developing an Organic Light-Emitting Diode, hereinafter referred to as an OLED, having an efficiency of 1.5 lm/W by using organic thin film materials.
Since then, the OLED has been commercialized and in the spotlight as a next-generation display element for having several advantages, such as vivid color reproduction, high contrast ratio, fast response rate, and wide view angle.
The OLED may be driven by voltage or current. In the former case, change in luminance may increase due to a deviation in the current-voltage characteristic of the OLED. Hence, to avoid such problem, it is common to drive the OLED by current despite the low driving speed.
A driving circuit for driving the OLED by current comprises a driving Thin Film Transistor (TFT), which applies a driving current to the OLED.
Although it is desirable to design electrical characteristics, such as the mobility or the threshold voltage of the driving TFT and, to be uniform in all pixels, a deviation in luminance for each pixel, caused by non-uniformity in processing and change in the threshold voltage (VTH) due to stress voltage, occurs.
To solve such problem, the inventor of the present invention has been continuously researching and developing while experiencing trial and error and finally completed the present invention.